You can find every content type here: http://www.iana.org/assignments/media-types/media-types.xhtml

The most common type are:

1. Type application

   application/EDI-X12
   
   application/EDIFACT
   
   application/javascript
   
   application/octet-stream
   
   application/ogg
   
   application/pdf
   
   application/xhtml+xml
   
   application/x-shockwave-flash
   
   application/json
   
   application/ld+json
   
   application/xml
   
   application/zip
   
   application/x-www-form-urlencoded
   
   

2. Type audio

   audio/mpeg
   
   audio/x-ms-wma
   
   audio/vnd.rn-realaudio
   
   audio/x-wav
   
   

3. Type image

   image/gif
   
   image/jpeg
   
   image/png
   
   image/tiff
   
   image/vnd.microsoft.icon
   
   image/x-icon
   
   image/vnd.djvu
   
   image/svg+xml
   
   

4. Type multipart

   multipart/mixed
   
   multipart/alternative
   
   multipart/related (using by MHTML (HTML mail).)
   
   multipart/form-data
   
   

5. Type text

   text/css
   
   text/csv
   
   text/html
   
   text/javascript (obsolete)
   
   text/plain
   
   text/xml
   
   

6. Type video

   video/mpeg
   
   video/mp4
   
   video/quicktime
   
   video/x-ms-wmv
   
   video/x-msvideo
   
   video/x-flv
   
   video/webm
   
   

7. Type vnd :

   application/vnd.oasis.opendocument.text
   
   application/vnd.oasis.opendocument.spreadsheet
   
   application/vnd.oasis.opendocument.presentation
   
   application/vnd.oasis.opendocument.graphics
   
   application/vnd.ms-excel
   
   application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
   
   application/vnd.ms-powerpoint
   
   application/vnd.openxmlformats-officedocument.presentationml.presentation
   
   application/msword
   
   application/vnd.openxmlformats-officedocument.wordprocessingml.document
   
   application/vnd.mozilla.xul+xml
   
   

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Type

The Content-Type entity header is used to indicate the media type of the resource.

In responses, a Content-Type header tells the client what the content type of the returned content actually is. Browsers will do MIME sniffing in some cases and will not necessarily follow the value of this header; to prevent this behavior, the header X-Content-Type-Options can be set to nosniff.

In requests, (such as POST or PUT), the client tells the server what type of data is actually sent.

It also needs to have a MIME type of its parsed value (ignoring parameters) of either application/x-www-form-urlencoded, multipart/form-data, or text/plain.